There are many situations where is it desirable to locate buried utilities such as pipes and cables. For example, before starting any new construction that involves excavation, worker safety and project economic concerns require the location and identification of existing underground utilities such as underground power lines, gas lines, phone lines, fiber optic cable conduits, cable television (CATV) cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually herein referred to as “buried objects.”
As used herein, the term “buried objects” includes objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, for example, as well as objects disposed below the surface of the ground. If excavation equipment such as a backhoe hits a high voltage line or a gas line, serious injury and property damage may result. Unintended severing of water mains and sewer lines generally leads to messy and expensive cleanup efforts. The unintended destruction of power and data cables may seriously disrupt the comfort and convenience of residents and bring huge financial costs to business. Accordingly, the art is replete with proposed solutions to the buried object locating problem.
A sonde typically includes a coil of wire wrapped around a ferromagnetic core that is packaged for insertion into a buried nonconductive conduit, such as a plastic utility runway or a concrete water pipe. Still other buried objects, such as conductive lines and pipes, may be located by first applying an external electromagnetic signal to the object to induce an alternating current therein, thereby energizing the object with a nonzero frequency magnetic field that may be detected by a magnetic sensor. For example, an external electrical signal source (transmitter) having a frequency in the range of approximately 4 Hz to 500 kHz has a well-known utility for energizing conductive objects by direct electrical coupling to permit their location. These examples of active and passive location of buried long conductors are also commonly described as “line tracing.”
Employing a directly-coupled external transmitter to induce an alternating current in a buried conductive object is useful, if the buried line is accessible for the conductive attachment of the transmitter output signal. When there is no conductive access to the buried conductor, such a transmitter may alternatively be used to indirectly induce an alternating current in the buried line, but this approach as used in the art has several well-known limitations.
Thus, improving the transmitter signal for direct or inductive coupling to a buried conductor by overcoming well-known deficiencies in the art would enhance the ability to locate the buried conductor. Improving transmitter reliability and reducing frequency drift, which is a well-known problem that eventually moves the transmitted pulse peak away from the pre-selected induction frequency, would likewise be beneficial, as would enhancing the transmitter output circuit quality (Q)-factor to improve the ratio of energy stored to energy lost per cycle, for example.
Accordingly, there is a need in the art for improved self-tuning inductive transmitters to solve the above problems as well as others.